Abstract

The Central Texas endemic freshwater mussel, Quadrula mitchelli (Simpson in Dall, 1896), had been presumed extinct until relict populations were recently rediscovered. To help guide ongoing and future conservation efforts focused on Q. mitchelli we set out to resolve several uncertainties regarding its evolutionary history, specifically its unknown generic position and untested species boundaries. We designed a molecular matrix consisting of two loci (cytochrome c oxidase subunit I and internal transcribed spacer I) and 57 terminal taxa to test the generic position of Q. mitchelli using Bayesian inference and maximum likelihood phylogenetic reconstruction. We also employed two Bayesian species validation methods to test five a priori species models (i.e. hypotheses of species delimitation). Our study is the first to test the generic position of Q.mitchelli and we found robust support for its inclusion in the genus Fusconaia. Accordingly, we introduce the binomial, Fusconaia mitchelli comb. nov., to accurately represent the systematic position of the species. We resolved F. mitchelli individuals in two well supported and divergent clades that were generally distinguished as distinct species using Bayesian species validation methods, although alternative hypotheses of species delineation were also supported. Despite strong evidence of genetic isolation within F. mitchelli, we do not advocate for species-level status of the two clades as they are allopatrically distributed and no morphological, behavioral, or ecological characters are known to distinguish them. These results are discussed in the context of the systematics, distribution, and conservation of F. mitchelli.

Keywords

Unionidae Species rediscovery Species delimitation Bayesian phylogenetics and phylogeography Fusconaia

Notes

Acknowledgments

Funding from the United States Fish and Wildlife Service Region 2, United States Geological Survey, Texas Department of Transportation, and Texas Comptroller helped make this work possible. We thank Peter Scott and Nathan Whelan for various discussions regarding Bayesian species delimitation and reconstruction. Mark Cordova, J. Harris, M. Johnson, S. McMurray, S. Oetker, E. Tsakiris, and K. Roe helped collect specimens. Kevin Skow and T. Snelgrove assisted with mapping and GIS. We gratefully acknowledge M. Bemis, L. Groves, A. Harris, B. Hershler, J. Slapcinsky, T. Lee for their assistance with the acquisition of loan material. Harry Lee provided assistance with addressing various nomenclatural issues. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the United States Government.

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